Condoms reduce transmission of HSV 2 by 65% so not perfect.
Antibiotics would not influence the test, no.
So this partner has actually been tested for HSV 2 or they believe that they don’t? Very different things.
The thing is, you are still very early for testing for HSV antibody. If this partner has actually been tested for HSV 2 and is known to be negative, then you need to wait 12 weeks from the last sexual contact before that to do the blot.
If the inhibition assay was done at least 12 weeks from any concerning encounter and is negative, there is good agreement between that result and a negative western blot